Radiation curable coating

ABSTRACT

A radiation curable coating composition for various substrates containing an adduct of acrylic acid and an epoxy resin (which may be modified with an anhydride, such as maleic anhydride), and a reactive acrylate monomer vehicle. The coating composition can be pigmented and can also contain additives commonly used in coatings, such as wetting agents and flow control agents. The coating composition does not require the usual hydrocarbon vehicles that give rise to air pollution problems. Surface gloss of a UV cured film obtained from a pigmented coating composition can be increased by using a photosensitizer combination of 2-chlorothioxanthone and a phenyl ketone, such as benzophenone. Adhesion of a cured coating is improved by replacing the tertiary amine co-sensitizer, at least in part, with dimethylaminoethyl acrylate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of copending application, Ser. No. 551,584, filed Feb. 20, 1975, now abandoned which is a continuation of application Ser. No. 471,412, filed May 20, 1974, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is directed to epoxy acrylate ester coatings, for substrates, that are curable with radiation.

2. Description of the Prior Art

British Pat. No. 1,241,851 describes a process for coating an article that comprises applying a film of an ethylenically unsaturated ester having hydroxyl groups and exposing it to ionizing radiation. No liquid vehicle is used.

The coating composition of this invention comprises a similar resin in a vehicle that is a reactive monomer. The vehicle, when the coating composition is exposed to radiation and set, reacts with the resin and becomes an integral part of the resultant coating.

SUMMARY OF THE INVENTION

This invention provides a coating composition that comprises an adduct of acrylic acid and an epoxy resin, or an anhydride modified adduct, and a reactive acrylate monomer. A photosensitizer and optionally, a tertiary amine co-sensitizer are used in the case of ultraviolet (UV) light cured coatings.

It also provides a UV curable pigmented coating composition that contains a photosensitizer combination of 2-chlorothioxanthone and a phenyl ketone.

It further provides a UV curable coating composition that affords improved film adhesion, in which at least part of the tertiary amine co-sensitizer is replaced with dimethylaminoethyl acrylate.

It still further provides substrates coated with the aforedefined coating compositions.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Prior practice has been to coat substrates, such as metals useful for container manufacture, with a variety of coating compositions comprising heat curable resinous components and non-reactive, volatile organic solvents that are removed from the coating during the curing process. Recent restrictions on allowable atmospheric pollutants, the shortage of organic solvents, and the shortage of fuels useful for firing curing ovens has created a need for coating compositions which can be cured with lower energy requirements and which eliminate the need for non-reactive organic solvents.

The coating compositions of this invention comprise an adduct, a reactive monomer vehicle, and optionally a photosensitizer. The adduct is an adduct of acrylic acid and an epoxy resin or said adduct further modified by reaction with an anhydride.

The epoxy resin can be any polyglycidyl ether of polyhydric organic compounds, especially polyhydric phenols. Particularly preferred are the glycidyl ethers of bisphenols, a class of compounds which are constituted by a pair of phenolic groups interlinked through an intervening aliphatic bridge. While any of the bisphenols may be used, the compound 2,2-bis (p-hydroxyphenyl) propane, commonly known as bisphenol A, is more widely available in commerce and is preferred. While polyglycidyl ethers can be used, diglycidyl ethers are preferred.

Depending upon whether the epoxy resin is substantially monomeric or polymerized to some degree, the preferred epoxy resins will have an epoxy equivalent weight of between about 170 and about 2,000 and an epoxy value between about 0.60 and about 0.05. The preferred epoxy resins, i.e., those made from bisphenol A, will have two epoxy groups per molecule. Accordingly, the stoichiometric amount of acrylic acid to form a diacrylate adduct would be two moles of acid for each two epoxy groups. In practice, however, it is preferred to use slightly less acid than the amount necessary to cover both epoxy groups to be certain that there is no free acrylic acid remaining in the reaction product. Free acid would contribute to excessive volatility of deposited films, while minor amounts of free epoxy are not objectionable. Therefore, the amount of acrylic acid reacted can be between about 1.85 moles to 2.0 moles of acid per two epoxy groups. The esterification reaction between the acrylic acid and epoxy resin is carried out at an esterification temperature, e.g. between about 90° C. and about 110° C. Esterification is continued until an acid number of 5-15 is obtained. This reaction ordinarily takes place in 8-15 hours.

In another embodiment of this invention, the epoxy diacrylate is further reacted with an anhydride. Maleic anhydride is preferred but other anhydrides are contemplated for this purpose, such as citraconic anhydride, succinic anhydride, ethylsuccinic anhydride, amylenesuccinic anhydride, itaconic anhydride, glutaric anhydride, Δ4-tetrahydrophthalic anhydride, phthalic anhydride, hemimellitic anhydride, trimellitic anhydride, and pyromellitic anhydride. The amount of anhydride used will be between about 0.1 and about 1.0 mole anhydride per mole diacrylate resin. This reaction is generally carried out at temperatures between about 80° C. and about 90° C. The reaction is considered complete when the alcoholic KOH and aqueous KOH acid numbers agree, i.e., about 10-40. This evidences a complete absence of anhydride functionality.

The esterification reaction and the further reaction with anhydride can occur without the aid of a catalyst. However, catalysts are preferred such as tertiary amines; quaternary ammonium hydroxides, such as benzyltrimethylammonium hydroxide; N,N-dimethylaniline; N,N-benzylmethylamine; triethylamine; and KOH. It is also advantageous to use small amounts of hydroquinone as a polymerization inhibitor.

The epoxy diacrylate or the anhydride modified epoxy diacrylate, prepared as aforedescribed, is then dissolved in a reactive monomer vehicle to prepare the coating composition. The reactive monomer vehicle contemplated herein is a monofunctional ester of acrylic acid having from 4 to about 20 carbon atoms. The acrylate ester can be an alkyl or hydroxyalkyl acrylate, such as methyl acrylate, ethylacrylate, hydroxyethyl acrylate, propyl acrylate, isopropyl acrylate, hydroxypropyl acrylate, butyl acrylate, isobutyl acrylate, amyl acrylate, hexyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, dodecyl acrylate, tetradecyl acrylate, and hexadecyl acrylate. Also contemplated are the acrylic esters of the well known class of ether alcohols having the formula: ROCH₂ CH₂ OH, wherein R is C₁ -C₆ alkyl or phenyl, i.e. the Cellosolves. Examples of such esters are methoxyethyl acrylate (Methylcellosolve acrylate), ethoxyethyl acrylate (Cellosolve acrylate), butoxyethyl acrylate (Butylcellosolve acrylate), isobutoxyethyl acrylate (Isobutylcellosolve acrylate), hexoxyethyl acrylate (Hexylcellosolve acrylate), and phenoxyethyl acrylate (Phenylcellosolve acrylate). The contemplated reactive monomer vehicle can be designated by the formula: CH₂ =CHCOOR, wherein R is C₁ -C₁₅ alkyl or hydroxyalkyl; C₂ H₄ OR', wherein R' is C₁ -C₆ alkyl or phenyl; ##STR1## wherein R" is C₁ -C₄ alkylene and R'" is C₁ -C₄ alkyl, phenyl, or cresyl; ##STR2## wherein R'" is C₁ -C₄ alkyl, phenyl, or cresyl; and ##STR3## wherein R" is C₁ -C₄ alkyl, R"" is H or C₁ -C₃ alkyl, and x is an integer from 1 to 10.

In the case above when R is ##STR4## the reactive monomer is a carbamoyloxyalkyl acrylate. Compounds of this class are readily prepared by well known methods for preparing carbamates. Thus, a hydroxyalkyl acrylate, e.g., hydroxyethyl acrylate, can be reacted with an isocyanate, e.g., butyl isocyanate, phenyl isocyanate, or cresyl isocyanate to form the carbamoyloxyalkyl acrylate, in the presence of a catalyst, e.g., dibutyltin dilauryl. Alternatively, the carbamoyloxyalkyl acrylate can be prepared by first reacting a hydroxyalkyl acrylate, e.g., hydroxyethyl acrylate, with phosgene in the presence of a base to give a chloroformate intermediate and then further reacting this intermediate with an amine, e.g., ethylamine, butylamine, or aniline, in the presence of a tertiaryamine acceptor for HCl, e.g., triethylamine. Reference should be made to U.S. Pat. No. 3,288,673 for a description of the techniques involved, described therein with regard to forming carbamates from hydroxybenzothiophenes.

When R is ##STR5## the reactive monomer is an alkyl 2-hydroxypropyl ether acrylate. Compounds of this class are readily prepared by the well known addition esterification reaction of acrylic acid with an alkyl glycidyl ether, e.g. butyl glycidyl ether.

When R is ##STR6## the reactive monomer will be a polyoxyethylene ether of alkyl acrylate. Generally, these compounds can be prepared by reacting a hydroxyalkyl acrylate with an alkylene oxide (1,2-epoxyalkane), e.g. ethylene oxide, 1,2-epoxypropane, or 1,2-epoxybutane, using a molar ratio of acrylate:alkylene oxide of 1:1 to about 10:1, at about 30°-75° C, and using an initiator such as borontrifluoride etherate. In the specific case wherein the alkylene and the alkyl groups are all ethyl, the acrylate can be prepared by monoesterification of a poly(oxyethylene) glycol (commercially available under the registered trademark Carbowax) with acrylic acid or acryloyl chloride.

Typical examples of carbamoyloxyalkyl acrylates, alkyl or aryl, 2-hydroxypropyl ether acrylates (alkoxy-2-hydroxypropyl acrylates), and hydroxy polyoxyalkylene ethers of alkyl acrylates include butylcarbamoylethyl acrylate, phenylcarbamoylbutyl acrylate, cresylcarbamoylpropyl acrylate, butoxy-2-hydroxypropyl acrylate, phenoxy-2-hydroxypropyl acrylate, cresoxy-2-hyroxypropyl acrylate, hydroxy penta(oxypropyl) ether of ethyl acrylate, hydroxy deca(oxyethylene) ether of butyl acrylate, and hydroxy hexa(oxybutylene) ether of propyl acrylate.

The reactive monomer vehicle can contain a minor amount (up to about 20 weight percent) of a polyfunctional acrylate, e.g. neopentylglycol diacrylate, but it is predominantly monofunctional. In some formulations, the reactive monomer vehicle may have sufficiently high viscosity that it renders the formulation too viscous for some applications. In such cases, it will be desirable to control the viscosity by adding a more fluid vinyl monomer or acrylate ester to the reactive monomer vehicle. Typically, the addition of about 5 to 10 weight percent of a vinyl monomer, e.g. N-vinyl pyrrolidone, to the reactive monomer vehicle can be utilized to afford satisfactory viscosity control. Additionally, it has been found that N-vinyl pyrrolidone increases the hardness of the cured film.

The coating composition is cured by exposure to radiation. When the radiation used is electron beam radiation a photosensitizer is not needed, but when ultraviolet light is used, a photosensitizer is needed. Suitable sensitizers include acetophenone, 4'-t-butyl-2,2,2-trichloroacetophenone, 4'phenoxy-2,2-dichloroacetophenone, benzophenone, xanthone, benzoin isobutyl ether, benzoin isopropyl ether, and 2-chlorothioxanthone. 2-Chlorothioxanthone is preferred, particularly when the formulation is pigmented. A tertiary amine co-sensitizer may also be used in the UV curable coating formulation. It is not essential, but it serves to speed up the cure rate. In order to realize this function, it is necessary to have free amine present. Accordingly, the amine concentration range when a co-sensitizer is used, is from about 1.25 to about 3 times the amount required to neutralize free acidity. The amount required for neutralization can be readily calculated from the determined acid number of the resin. The tertiary amines are normally liquid trialkylamines, trialkanolamines, or tertiary mixed alkylalkanolamines. Non-limiting examples of such amines are triethylamine, triisopropylamine, tributylamine, trihexylamine, tri-2-ethyl-hexylamine, tridodecylamine, methyldiethanolamine, dimethylethanolamine, 2-hydroxyethyldiisopropylamine, and triethanolamine.

The coating compositions described so far produce clear coatings and are useful as such.

Although a pigment is not necessary, it is preferred to incorporate a pigment into the coating composition of this invention. The preferred pigment is titanium dioxide for white base coats, but any well known filler pigment can be used, such as zinc oxide, bentonite, silica, ochers, and chrome yellows or greens.

Depending upon whether the coating composition is pigmented or not, the broad and preferred ranges of concentration of the components are as set forth in the following Table I.

                  TABLE I                                                          ______________________________________                                                Broad, Wt. %  Preferred, Wt. %                                                             Not               Not                                       Component                                                                               Pigmented Pigmented Pigmented                                                                              Pigmented                                 ______________________________________                                         Adduct Resin                                                                            10-30     10-75     15-30   10-50                                     Reactive                                                                       Monomer  40-60     20-90     30-50   50-90                                     Vehicle                                                                        Tertiary 0.5-6     0-6       2-4     0-4                                       Amine                                                                          Sensitizer                                                                              0.1-6     0.1-6     0.5-1   0.5-5                                     (if used)                                                                      ______________________________________                                    

The coating composition is applied to a usual substrate, metal, paper, leather, cloth, etc. using any of the usual methods of application, including wiping, spraying and rollcoat application. Suitable metallic substrates include aluminum, steel, and tin-plated steel. The rate of application will be sufficient to apply the coating at about 1-20 mg/sq. in. After application, the coating is set by exposure to radiation for between about 0.01 second and about 30 seconds. In some cases, the coating will be set by short exposure to radiation, e.g. less than one second, which is sufficient to set the film so that it will accept inks and/or a wet-ink varnish. Following the printing or varnishing opertion, these coats may be further set by baking at about 250° F. to 450° F. for between about 3 seconds and about 5 minutes.

Suitable sources of radiation are ultraviolet light or electron beam radiation. Preferably, an ultraviolet light of a wave length below 4000 Angstrom Units is used. The electron beam radiation is obtained from high energy electrons produced by high voltage electron accelerator, resonant transformers, transformer rectifiers, micro-wave waveguide linear accelerator, and synchrotrons.

The following examples demonstrate the preparation of adducts and coatings containing them, in accordance with this invention.

EXAMPLE 1

Using a vessel equipped with an agitator, a reflux condenser, an inert gas inlet and a charging port, there was charged 660 grams Epon 828. Epon 828 is a diglycidyl ether of bisphenol A having an epoxy equivalent weight of about 185-192 and an epoxide value of 0.50-0.54. Through the gas inlet was introduced a nitrogen flow which was maintained throughout the resin preparation cycle. While under agitation, 238 grams glacial acrylic acid was added and stirred until epoxy resin dissolved. Upon dissolution of the acrylic acid, 1.3 grams triethyl amine and 0.1 gram hydroquinone were added. Under continued agitation, heat was raised to 205°-212° F. and held at this temperature until an acid number of 5-10 was obtained (approximately 10 hours). Temperature was reduced to 150°-160° F. and 600 grams hydroxypropyl acrylate was added and the mixture was stirred until uniform. The final product was a clear solution of prepolymer in monomer at a 60/40 weight ratio.

EXAMPLE 2

Using a vessel equipped as in the previous example, there were charged 7200 g. Epon 828, 2590 g. glacial acrylic acid, 15 g. triethyl amine and 1.2 g. hydroquinone. Agitation was started along with nitrogen flow and the mixture was heated to 100° C. Temperature was maintained at 95°-100° C. until an acid number of 5-10 was obtained; at this point, was added 432 g. maleic anhydride and the temperature was held at 90° C. until the acid number, as determined by alcoholic KOH and aqueous KOH, agreed, thereby indicating the complete absence of anhydride functionality. The normal time for this phase of the resin preparation was 1.5 hours. At this point, was added 6835 g. hydroxypropyl acrylate. The final product was a 60/40 ratio of preopolymer/monomer having a viscosity of 850-900 cp at 80° F. a weight/gallon of 9.5 pounds/gallon, and an acid value of 28-35. The molar ratio of maleic anhydride to epoxy resin was 0.25.

The following Examples 3 and 4 demonstrate coatings curable by electron beam radiation.

EXAMPLE 3

In a suitable sized high speed disperser, were thoroughly mixed 27.1 pounds of the product from Example 1 and 42.8 pounds titanium dioxide pigment and the mixture was stirred until a fineness of grind of 7 or better was obtained. Then were added 31.4 pounds hydroxypropyl acrylate, and 20.2 pounds of the product from Example 1 and the mixture was stirred until uniform. The resultant finish had a pigment/binder ratio of 0.52/1 and a prepolymer/total binder ratio of 0.4/1.

EXAMPLE 4

Using the equipment of Example 3, were thoroughly mixed 27.3 pounds of the resin solution of Example 2, and 42.9 pounds of titanium dioxide pigment. Continued high speed agitation until a fineness of grind of 7 minimum was obtained. Agitation was continued but at slower speed, while adding 10.0 pounds of resin solution of Example 2 and 17.5 pounds of hydroxypropyl acrylate. This was stirred until uniform. The resultant finish had a pigment/binder ratio of 0.78/1 and a prepolymer/total binder ratio of 0.4/1.

EXAMPLE 5

To a suitable sized pebble mill, were charged one pound 2-chlorothioxanthone and 2 pounds hydroxypropyl acrylate. This was ground for 24 hours, until thoroughly dispersed. The product is suited for use as a photoinitiator for pigmented finishes.

EXAMPLE 6

In a suitably sized high speed disperser were thoroughly mixed 27.1 pounds of the product from Example 1, 42.8 pounds titanium dioxide pigment, and 1.5 pounds of the product of Example 5. l This was stirred until a fineness of grind of 7 or better was obtained. Then, were added 31.4 pounds hydroxypropyl acrylate, 2.0 pounds methyldiethanolamine and 20.2 pounds of the product of Example 1. The mixture was stirred until uniform. The resultant finish had a pigment/binder ratio of 0.52/1 and a prepolymer/total binder ratio of 0.4/1.

EXAMPLE 7

Using the equipment of Example 6, were thoroughly mixed 27.3 pounds of the resin solution of Example 2, 42.9 pounds of titanium dioxide pigment, and 0.8 pounds of 2-chlorothioxanthone. High speed agitation was continued until a fineness of grind of 7 minimum was obtained. Agitation was continued but at slower speed while adding 10.0 pounds of resin solution of Example 2, 17.5 pounds of hydroxypropyl acrylate, and 1.5 pounds of methyldiethanolamine. This was stirred until uniform. The resultant finish had a pigment/binder ratio of 0.78/1 and a prepolymer/total binder ratio of 0.4/1.

EXAMPLES 8 through 27

In Table II are set forth data on various coatings prepared using the techniques and methods set forth in Examples 1 through 7. Each coating was applied to various substrates, cured by ultraviolet light (UV) or electron beam (EB), and tested for film properties. The adhesion test is carried out by cross-hatching a coated area with individual score lines approximately 1/16 inch apart. Then Scotch tape is firmly applied to the cross-hatched area and removed with a quick snap. The amount of coating remaining on the panel is observed visually and rated on a percentage basis. Pasteurization is carried out by immersing the coated panels in water at 155° F. for 30 minutes. Then, the panels are wiped dry with an absorbent towel and the adhesion test is carried out as aforedescribed.

In Table II, the following abbreviations are used:

    ______________________________________                                         1004    =     Epon 1004 Reaction product epichlorohydrin                                     and bisphenol A. M.W. about 1400, Epoxide                                      value 0.10-0.12.                                                 828     =     Epon 828 Diglycidylether of bisphenol A.                                       M.W. about 350-400. Epoxide value 0.50-                                        0.54.                                                            A       =     2 moles acrylic acid per mole epoxy                              M       =     .25 moles maleic anhydride per mole epoxy                        HPA     =     Hydroxypropyl Acrylate                                           HEA     =     Hydroxyethyl Acrylate                                            2-EHA   =     2-Ethylhexyl Acrylate                                            MDEOA   =     Methyldiethanolamine                                             TEOA    =     Triethanolamine                                                  cps     =     Centipoise                                                       Al      =     Aluminum                                                         CCO     =     Chrome-chrome oxide treated steel                                CDC5    =     #5 grade of tinplate steel                                       TiO.sub.2                                                                              =     Titanium Dioxide                                                 THP     =     Δ 4-Tetrahydrophthalic anhydride                           CTX     =     2-Chlorothioxanthone                                             Monomer =     Reactive monomer vehicle                                         UV-25   =     Ultraviolet light at line speed 25 ft./min                                     per lamp.                                                        EB-2    =     Electron beam radiation at 2 megarad dosage                      ______________________________________                                    

                                      TABLE II                                     __________________________________________________________________________     VISCOSITY-ADHESION-GLOSS-LEVELING EFFECTS FOR VARIOUS                          LEVELS OF EPOXY MOLE WEIGHT AND ANHYDRIDE                                      __________________________________________________________________________     Composition, Wt. %                       Viscosity cps at                      Resin         Monomer  TiO.sub.2                                                                          CTX Amine     shear rate                            Ex.                                                                               Type   Wt. %                                                                              Type Wt. %                                                                              Wt. %                                                                              Wt. %                                                                              Type  Wt. %                                                                              222 sec.sup.-1                                                                       .0028 sec.sup.-1                __________________________________________________________________________      8  828/A/M                                                                              23.0                                                                               HPA  29.7                                                                               42   .5 MDEOA 4   615   18,000                           9  828/A/M                                                                              23.2                                                                               HPA  34.8                                                                               42  --  --    --  600   10,000                          10  828/A/M                                                                              42  HPA  53  --  1.0 MDEOA 4   200   200                             11  828/A/M                                                                              44  HPA  56  --  --  --    --  250   300                             12  828/A 22.8                                                                               HPA  33.4                                                                               42  1.0 MDEOA 4   375   29,000                          13  828/A 23.2                                                                               HPA  34.8                                                                               42  --  --    --  400   60,000                          14  828/A 53  HPA  44  --  1.0 MDEOA 2   200   300                             15  828/A 45  HPA  55  --  --  --    --  150   200                             16 1004/A/M                                                                              20  HPA  41.7                                                                                 33.3                                                                             1.0 MDEOA 4   1000  2,460                           17 1004/A/M                                                                              20  HPA  46.7                                                                                 33.3                                                                             --  --    --  1200  4,000                           18 1004/A/M                                                                              30  HPA  66.5                                                                               --   .5 MDEOA 3   400   400                             19 1004/A/M                                                                              30  HPA  70  --  --  --    --  500   600                             20 1004/A 20  HPA  42.2                                                                                 33.3                                                                             1.0 MDEOA 4   900   15,000                          21 1004/A 20  HPA  46.7                                                                                 33.3                                                                             --  --    --  900   45,000                          22 1004/A 30  HPA  66.5                                                                               --   .5 MDEOA 4   350   350                             23 1004/A 30  HPA  70  --  0   --    --  450   550                             24  828/A 23.2                                                                               HEA  30.3                                                                               42   .5 MDEOA 4   500   35,000                          25  828/A 28.6                                                                               HPA  25.6                                                                               42  1.0 TEOA  2   1200  60,000                          26  828/A/M                                                                              23.0                                                                                HPA/                                                                               14.6/                                                                              42  1.0 MDEOA 4   670   156,000                                       2-EHA                                                                               14.6                                                        27  828/A/THP                                                                            23.2                                                                               HPA  30.3                                                                               37   .5 MDEOA 4   244   24,00                           __________________________________________________________________________               Film Properties                                                                % Adhesion after                                                                           % Adhesion after                                         Cure      bake, 5'-350° F.                                                                    Pasteurization                                                                             60° Gloss                             Ex. Condition                                                                            Al  CCO CDC5                                                                               Al  CCO CDC5                                                                               %    Leveling                                __________________________________________________________________________      8  UV-25 100 100 25  100 100 0   30   Good                                     9  EB-2  100 100 25  100 100 0   90   Good                                    10  UV-25 100 0   0   100 0   0   80   Excellent                               11  EB-2  100 0   0   100 0   0   95   Excellent                               12  UV-25 100 0   0   100 0   0   50   Poor                                    13  EB-2  100 0   0   100 0   0   90   Poor                                    14  UV-25 0   0   0   0   0   0   80   Excellent                               15  EB-2  0   0   0   0   0   0   95   Excellent                               16  UV-25 100 100 100 100 100 50  60   Excellent                               17  EB-2  100 100 100 100 100 50  90   Excellent                               18  UV-25 100 100 100 100 100 0   80   Excellent                               19  EB-2  100 100 100 100 100 0   90   Excellent                               20  UV-25 100 100 0   100 100 0   55   Fair                                    21  EB-2  100 100 0   100 100 0   90   Fair                                    22  UV-25 100 0   0   100 0   0   80   Excellent                               23  EB-2  100 0   0   100 0   0   90   Excellent                               24  UV-25 100 100 25  100 100 0   55   Fair                                    25  UV-25 100 100 25  100 100 0   65   Good                                    26  UV-25 100 100 100 100 100 0   15   Fair                                    27  UV-25 100 100 100 100 50  0   60   Fair                                    __________________________________________________________________________

The results given in Table I indicate that:

(a) Increasing epoxy resin molecular weight improves adhesion to metals.

(b) Maleic anhydride adducts have better adhesion to metals and demonstrate better leveling than compositions containing resins containing no maleic anhydride.

(c) Coatings containing TiO₂ have better adhesion to metals than do coatings of identical composition but without TiO₂.

In the foregoing examples of UV curable coatings, an amine co-sensitizer was used. As indicated hereinbefore, the co-sensitizer is not necessary and in clear coatings it causes a discoloration that often is undesirable. In such a case, the amine co-sensitizer is omitted and the amount of sensitizer is increased. This is demonstrated in the following examples.

EXAMPLES 28 through 31

Coating compositions were prepared by admixing 40 weight percent of the diacrylate of Epon 828 (Example 1), 55 weight percent of hydroxypropyl acrylate, and 5 weight percent of a UV sensitizer. In each example, a different sensitizer was used, namely, benzoin isobutyl ether (BIBE); benzoin isopropyl ether (BIPE); 4'-t-butyl-2,2,2-trichloroacetophenone (BTA); and 4'-phenoxy-2,2-dichloroacetophenone (PDA). Each coating composition was coated on aluminum at a film thickness of about 3 mg./in.² and exposed to a 2-lamp (200 watts/inch) UV light unit at 25 FPM followed by a postbake of 3 min. at 350° F. to remove unreacted monomer. Each film was observed for film yield and pertinent data are set forth in Table III.

                  TABLE III                                                        ______________________________________                                         Example     Sensitizer    Film yield, %                                        ______________________________________                                         28          BIBE          85.6                                                 29          BIPE          90.1                                                 30          BTA           92.5                                                 31          PDA           93.1                                                 ______________________________________                                    

In the preceding examples, relatively short chain acrylate esters, e.g., hydroxypropyl acrylate, were generally used. The following examples demonstrate the use of other, longer chain acrylate esters.

EXAMPLES 32 through 36

Coating compositions were prepared by admixing 40 weight percent of the diacrylate of Epon 828 (Example 1), 55 weight percent of an acrylate ester reactive monomer, and as sensitizer either 5 weight percent BIBE or 5 weight percent BTA. In each composition, the reactive monomer was (A) butoxy-2-hydroxypropyl acrylate, (B) butylcarbamoylethyl acrylate, or (C) penta (oxyisopropyl) ether of ethyl acrylate. Each coating composition was coated on aluminum and cured as described in Examples 28-31. Pertinent data and film yield results are set forth in Table IV.

                  TABLE IV                                                         ______________________________________                                         Example  Monomer    Sensitizer Film yield, %                                   ______________________________________                                         32       A            BIBE     85                                              33       A          BTA        93                                              34       B            BIBE     88                                              35       B          BTA        96                                              36       C          BTA        90                                              ______________________________________                                    

The coating compositions that have been described and illustrated hereinbefore can be considered the "basic" coating compositions. It has been found that certain properties of the cured film can be markedly improved by incorporating additional chemicals into the basic coating compositions.

With the basic UV curable coating compositions, the gloss of the cured film is usually lower than desired, particularly at higher cure rates. This gloss can be markedly increased by using in the coating composition a sensitizer combination of 2-chlorothioxanthone and a phenyl ketone. Benzophenone is the preferred phenyl ketone, but other phenyl ketones are contemplated, such as acetophenone, propiophenone, and butyrophenone.

The following examples demonstrate this gloss improvement. In each example, using the techniques and methods of Examples 1-7, a pigmented coating composition (A) without benzophenone (Bzph) and (B) with benzophenone were coated on aluminum and exposed to UV at various cure speeds. The resulting films were tested for 60° gloss.

EXAMPLE 37

An epoxy diacrylate of Epon 828 was modified with 0.25 mole maleic anhydride per mole epoxy. This resin (Resin A) was admixed with hydroxypropyl acrylate, TiO₂ pigment, and sensitizers and co-sensitizers. The following tabulation sets forth amounts of components, pigment/binder ratio (P/B), resin/binder ratio (R/B), and pertinent test data.

    ______________________________________                                         Example TiO.sub.2 CTX       MDEOA   Resin A                                    ______________________________________                                         37A     36.6      0.9       3.6     24.5                                       37B     36.6      0.9       3.6     24.5                                       Example HPA       Bzph      P/B     R/B                                        ______________________________________                                         37A     34.4        0       .58     .39                                        37B     32.4      2.0       .58     .39                                        UV Cure Speed 25 FPM                                                                               No Bzph   2% Bzph                                                       Yield  90        90                                                            Gloss  79        88                                               ______________________________________                                    

EXAMPLE 38

An epoxy diacrylate of Epon 828 (Resin B) was admixed with hydroxypropyl acrylate, TiO₂ pigment, and sensitizers and co-sensitizers. The following tabulation set forth amounts of components and pertinent test data.

    ______________________________________                                         Example TiO.sub.2 Resin B   HPA      CTX                                       ______________________________________                                         38A     42.8      28.6      25.6    1.0                                        38B     41.5      27.7      24.8    1.0                                        Example MDEOA     Bzph      P/B     R/B                                        ______________________________________                                         38A     2.0         0       .75     .50                                        38B     3.0       2.0       .71     .475                                       UV Cure Speed, FPM  No Bzph   2% Bzph                                          25            Yield     94        91                                                         Gloss     95        95                                           50            Yield     91        87                                                         Gloss     77        93                                           100           Yield     87        84                                                         Gloss     39        90                                           ______________________________________                                    

EXAMPLE 39

An epoxy diacrylate of Epon 1004 was modified with 0.25 mole maleic anhydride per mole epoxy. This resin (Resin C) was admixed with hydroxypropylacrylate, TiO₂ pigment, and sensitizers and co-sensitizers. The following tabulation sets forth amounts of components and pertinent test data.

    ______________________________________                                         Example   TiO.sub.2  Resin C    CTX                                            ______________________________________                                         39A       33.3       20.0       1.0                                            39B       33.0       19.8       1.0                                            Example   MDEOA      HPA        Bzph                                           ______________________________________                                         39A       4.0        41.7         0                                            39B       4.0        41.2       1.0                                            UV Cure Speed, FPM                                                                                     No Bzph   2% Bzph                                      25            Yield     88        88                                                         Gloss     89        89                                           50            Yield     86        85                                                         Gloss     75        88                                           100           Yield     73        77                                                         Gloss     45        62                                           ______________________________________                                    

The preceding examples illustrate that benzophenone (a phenyl ketone) combined with 2-chlorothioxanthone has essentially no effect on film yield, but increases the gloss of pigmented UV curable coatings. Each sensitizer is used, as described hereinbefore, in amounts of between about 0.1% and about 2% by weight.

It has been found that adhesion of the cured coating to some substrates, particularly pasteurized adhesion (Past. Adh.), is improved by using dimethylaminoethyl acrylate (DMAEA) in the coating composition. In the case of EB curable coatings, the DMAEA is added to the coating composition in amounts of between about 0.5% and about 6% by weight. In the case of UV curable coatings the DMAEA is used in amounts of between about 0.5% and about 6% by weight to replace all or a part of the tertiary amine co-sensitizer.

EXAMPLE 40

Resin B (Example 38) was admixed with hydroxypropyl acrylate, 2-chlorothioxanthone, and MDEOA or DMAEA. Each coating was coated on aluminum panels and UV cured. The coated panels were subjected to adhesion tests. Amounts of components and test results are set forth in the following tabulation.

    ______________________________________                                         Example                                                                               Resin B  CTX     HPA    MDEOA   DMAEA                                   ______________________________________                                         40A    49.5     1.0     44.5   0       5                                       40B    50.0     1.0     47.0   2       0                                       50 FPM UV Cure                                                                        Film                                                                    Example                                                                               Yield    Adhesion     Past. Adh.                                        ______________________________________                                         40A    92       100          50                                                40B    89       20            0                                                ______________________________________                                    

EXAMPLE 41

Resin C (Example 39) was admixed with hydroxypropyl acrylate, 2-chlorothioxanthone, and MDEOA or DMAEA. Each coating was coated on aluminum panels and UV cured. The coated panels were subjected to adhesion tests. Amounts of components and test results are set forth in the following tabulation.

    ______________________________________                                         Example                                                                               Resin C  HPA      CTX   MDEOA   DMAEA                                   ______________________________________                                         41A    29.2     68.2     0.5   2       0                                       41B    29.2     68.2     0.5   0       2                                              UV Cure                                                                        Speed,    Film               Past.                                      Example                                                                               FPM       Yield      Adh.    Adh.                                       ______________________________________                                         41A    25        92         100     85                                                50        87         100     70                                         41B    25        89         100     100                                               50        87         100     100                                        ______________________________________                                    

EXAMPLE 42

Resin B (Example 38) was admixed with hydroxypropyl acrylate, TiO₂ pigment, 1.0% 2-chlorothioxanthone, and MDEOA or DMAEA. The P/B of each coating was 0.75 and the R/B was 0.40. Each coating was coated on metal panels and UV cured. The coated panels were subjected to adhesion tests. Results are set forth in the following tabulation.

    ______________________________________                                                        Viscosity, cp                                                   Example  Amine       222 sec.sup.-1                                                                             .0228 sec.sup.-1                              ______________________________________                                         42A      4% MDEOA    395         29,100                                        42B      5% DMAEA    283           564                                                50 FPM    Adhesion to                                                   Example  Yield       Al          CCO                                           ______________________________________                                         42A      89          100          0                                            42B      89          100         100                                           ______________________________________                                    

EXAMPLE 43

Resin B (Example 38) was admixed with hydroxypropyl acrylate, TiO₂ pigment, 1.0% 2-chlorothioxanthone, and MDEOA or DMAEA. The P/B of each coating was 0.75 and the R/B was 0.6. Each coating was coated on metal panels and UV cured. The coated panels were subjected to adhesion tests. Results are set forth in the following tabulation.

    ______________________________________                                         Example  Amine       222 sec.sup.-1                                                                            .0228 sec.sup.-1                               ______________________________________                                         43A      4% MDEOA    800        86,100                                         43B      5% DMAEA    598        14,800                                                50 FPM    Adhesion to                                                   Example  Yield       Al          CCO                                           ______________________________________                                         43A      88          100          0                                            43B      89          100         100                                           ______________________________________                                    

It will be noted from the preceding examples that the use of dimethylaminoethyl acrylate gives at least equivalent UV cure. It also provides improved adhesion, both dry and wet.

The following examples are illustrative of preferred coating compositions of this invention.

EXAMPLE 44

Using a reaction vessel equipped with an agitator, a reflux condenser, an inert gas inlet and a charging port, there were charged 525 g. Epon 1004 and 70 g. toluene. Heat, agitation, and slow inert gas flow were started. Temperature was raised to reflux to remove water (a pot temperature of 150° - 160° C.). The mixture was cooled to 80° - 85° C. and there were added 40 g. glacial acrylic acid, 1 g. triethyl amine and 0.1 g. hydroquinone. Temperature was raised to 95° - 100° C. for esterification and the reaction continued until an acid number of 8-13 was obtained. This was cooled to 80° - 95° C. and there was added 7 g. maleic anhydride. Temperature was held at 80° - 85° C. for 11/2 to 2 hours until alcoholic KOH and aqueous KOH acid numbers agreed (10-15). Heat source was removed and 175 g. hydroxypropyl acrylate was added. The mixture was reheated to 80° - 85° C. and vacuum applied for toluene removal. Remove heat and add an additional 182 g. hydroxypropyl acrylate. The final product had a viscosity of 45-50,000 cp., a wt./gal. of 9.6 lb., an acid number of 10.5 and a total solids of approximately 97%. This resin was used in the formulations of Examples 45-47 (amounts are wt. % of formulation):

    ______________________________________                                         EXAMPLES 45 - 47 (Clear Finishes)                                              Ingredient        45       46       47                                         ______________________________________                                         Example 44 composition                                                                           40.3     56.4     33.2                                       Hydroxypropyl acrylate                                                                           56.3     40.2     37.6                                       Phenylcellosolve acrylate                                                                        --       --       21.8                                       Methyldiethanolamine                                                                              1.9      1.9      2.9                                       Dimethylaminoethyl acrylate                                                                      --       --        3.5                                       2-Chlorothioxanthone                                                                              0.5      0.5      0.5                                       Fluorocarbon wetting agent                                                                       --       --        0.5                                       Silicone lubricant                                                                                1.0      1.0     --                                         Viscosity (seconds #4                                                           Ford Cup)        50 - 60  175 - 225                                                                               30 - 35                                    Wt./gal. (lb.)    9.04     9.40     8.95                                       ______________________________________                                    

Examples 45 and 46 were formulated as an abrasion resistant coating for can bottoms, which is applied by a wiping action and given a UV treatment of 1-2 seconds with no post bake required.

Example 47 was formulated as a coating for flat sheet and is suitable for rollcoat application and given 1 second exposure to UV radiation, followed by a 10 minute oven bake at 340°-400° F. The Phenylcellosolve acrylate in Example 47 imparts improved corrosion resistance and flexibility.

EXAMPLE 48

There were charged 312 g. of an epoxy diacrylate made from Epon 828 and acrylic acid, 430 g. titanium dioxide, 198 g. Cellosolve acrylate, 10 g. 2-chlorothioxanthone, 40 g. dimethylaminoethyl acrylate and 10 g. benzophenone to a suitably sized pebble mill and ground to a fineness of 7 when measured on a Hegman fineness of grind gauge. Grind time is 24-48 hours. The final product was a white finish suitable for rollcoat application on flat sheet. The finish has a viscosity of 90-100 sec. #4 Ford Cup and a weight per gallon of 13.1-13.3 pounds. It is normally applied at 10 mg./sq. in. and cured using a 1 sec. UV exposure followed by a 6 minute bake at 325° F. After the UV exposure, the film was sufficiently set to accept inks and a wet ink varnish. The 6 min. at 325° F. bake indicated above followed inking and varnishing operations.

It will be noted that in Examples 47 and 48, dimethylaminoethyl acrylate was used. This compound has a tertiary amine functionality. Thus, as aforedescribed, it can replace the tertiary amine (used to speed up the cure rate) partially (Example 47) or entirely (Example 48). This compound also has reactive ethylenically unsaturated functionality (acrylate) and therefore acts as a reactive monomer. Its use affords a coating composition having improved rheology, as evidenced by better flow characteristics, and the cured coating has improved adhesion to metal substrates. The addition of benzophenone to the coating composition (Example 48) improves the gloss of the pigmented finish.

Other well known adjuvants may be added to the coating composition such as flow control agents and waxes. Waxes, if used, are added as slurries or emulsions of petroleum (paraffin) wax, natural waxes such as montan wax, beeswax, and carnauba wax, or synthetic waxes such as polyethylene wax.

Although the present invention has been described with preferred embodiments, it is to be understood that modifications and variations may be resorted to, without departing from the spirit and scope of this invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the appended claims. 

What is claimed is:
 1. A radiation curable coating composition that comprises, by weight of said composition, 10-75% of a diacrylate of a diglycidyl ether of a bisphenol, or of a diacrylate of a diglycidyl ether of a bisphenol further esterfied with 0.1-1 mole, per mole of said diacrylate, of a dicarboxylic acid anhydride to form an esterified product having an acid number of 10-40, and 25-90% of an ester of acrylic acid.
 2. The coating composition of claim 1, wherein said bisphenol is bisphenol A.
 3. The coating composition of claim 1, wherein said anhydride is maleic anhydride.
 4. The coating composition of claim 2, wherein said anhydride is maleic anhydride.
 5. The coating composition of claim 2, wherein said anhydride is Δ4-tetrahydrophthalic anhydride.
 6. The coating composition of claim 1, wherein said ester is hydroxypropyl acrylate.
 7. The coating composition of claim 2, wherein said ester is hydroxypropyl acrylate.
 8. The coating composition of claim 3, wherein said ester is hydroxypropyl acrylate.
 9. The coating composition of claim 4, wherein said ester is hydroxypropyl acrylate.
 10. The coating composition of claim 1, wherein said ester is hydroxyethyl acrylate.
 11. The coating composition of claim 2, wherein said ester is hydroxyethyl acrylate.
 12. The coating composition of claim 1, wherein said coating is curable by UV light and contains, by weight of said composition, 0.1-6% of a photosensitizer and 0-6% of a tertiary amine co-sensitizer.
 13. The coating composition of claim 12, wherein said photosensitizer is 2-chlorothioxanthone and said tertiary amine is methyldiethanolamine.
 14. The coating composition of claim 8, wherein said coating is curable by UV light and contains, by weight of said composition, 0.1-6% of 2-chlorothioxanthone and 0-6% of methyldiethanolamine.
 15. The coating composition of claim 9, wherein said coating is curable by UV light and contains, by weight of said composition, 0.1-6% of 2-chlorothioxanthone and 0-6% of methyldiethanolamine.
 16. A coating composition of claim 11, wherein said coating is curable by UV light and contains, by weight of said composition, 0.1-6% of 2-chlorothioxanthone and 0-6% of methyldiethanolamine.
 17. The coating composition of claim 1, wherein said coating is curable by UV light and contains, by weight of said composition, 0.1-6% of 2-chlorothioxanthone and 0-6% of triethanolamine.
 18. The coating composition of claim 2, wherein said coating is curable by UV light and contains, by weight of said composition, 0.1-6% of 2-chlorothioxanthone and 0-6% of triethanolamine.
 19. The coating composition of claim 1, wherein said coating contains a pigment.
 20. The coating composition of claim 1, wherein said coating contains titanium dioxide pigment.
 21. The coating composition of claim 6, wherein said coating contains titanium dioxide pigment.
 22. The coating composition of claim 9, wherein said coating contains titanium dioxide pigment.
 23. The coating composition of claim 12, wherein said coating contains titanium dioxide pigment.
 24. The coating composition of claim 14, wherein said coating contains titanium dioxide pigment.
 25. The coating composition of claim 15, wherein said coating contains titanium dioxide pigment.
 26. The coating composition of claim 16, wherein said coating contains titanium dioxide pigment.
 27. The coating composition of claim 18, wherein said coating contains titanium dioxide pigment.
 28. A substrate coated with the coating composition of claim
 1. 29. A metal substrate coated with the coating composition of claim
 2. 30. A metal substrate coated with the coating composition of claim
 4. 31. A metal substrate coated with the coating composition of claim
 9. 32. A metal substrate coated with the coating composition of claim
 14. 33. A metal substrate coated with the coating composition of claim
 21. 34. A metal substrate coated with the coating composition of claim
 20. 35. A metal substrate coated with the coating composition of claim
 22. 36. A metal substrate coated with the coating composition of claim
 27. 37. The coating composition of claim 1, wherein said ester is a carbamoyloxyalkyl acrylate.
 38. The coating composition of claim 2, wherein said ester is a carbamoyloxyalkyl acrylate.
 39. The coating composition of claim 4, wherein said ester is a carbamoyloxyalkyl acrylate.
 40. The coating composition of claim 1, wherein said ester is butylcarbamoyloxyethyl acrylate.
 41. The coating composition of claim 2, wherein said ester is butylcarbamoyloxyethyl acrylate.
 42. The coating composition of claim 12, wherein said photosensitizer is benzoin isobutyl ether.
 43. The coating composition of claim 12, wherein said photosensitizer is benzoin isopropyl ether.
 44. The coating composition of claim 12, wherein said photosensitizer is 4'-t-butyl-2,2,2-trichloroacetophenone.
 45. The coating composition of claim 42, wherein said ester is butylcarbamoylethyl acrylate.
 46. The coating composition of claim 43, wherein said ester is butylcarbamoylethyl acrylate.
 47. The coating composition of claim 44, wherein said ester is butylcarbamoylethyl acrylate. 